The invention relates to a dry-running twin-shaft vacuum pump with at least one pumping chamber, with a pair of rotors situated in the pumping chamber and borne by the shafts, with a drive housing which is associated with one of the two ends of the pumping chamber, and with mountings which are situated in the section of wall of the drive housing facing the pump chamber and support the two shafts which pass through this wall section.
"Dry-running" vacuum pumps are pumps whose pump chambers contain no lubricant or sealants. Their advantage lies in the fact that they can produce vacuums completely free of hydrocarbons. However, it is impossible to dispense with the lubrication of the bearings of the shafts which bear the pistons rotating in the pump chambers. In dry-running pumps, therefore, it is necessary to assure an effective separation of the bearing chambers from the pump chambers. At the one end of the pump the shafts reach all the way into the drive housing in which a drive synchronizing the rotor motion is situated. Also, the sealing off of the oil containing drive chamber from the adjacent pump chamber must be assured.
On account of their particular property of being able to produce hydrocarbon-free vacuums, dry-running twin-shaft vacuum pumps are often used in the semiconductor industry, namely in apparatus in which etching or coating processes are performed under vacuum. The gases used or formed in these processes are often toxic. Maintenance or service operations are therefore decidedly complicated by decontamination or the contaminated parts of the pump.
EU-A-290,662 has disclosed a twin-shaft vacuum pump of the kind mentioned above. The drive housing adjoining the discharge-end pumping chamber functions simultaneously as a bearing plate. Consequently contamination of parts of the drive housing is unavoidable. Before performing installation work on the pump, therefore, these parts of the drive housing must also be contaminated, which additionally complicates maintenance.
The present invention is addressed to the problem of creating a twin-shaft vacuum pump of the kind described above, in which a safe separation between the drive chamber and the adjacent pumping chamber will be assured and in which maintenance and installation operations can be performed in a substantially simpler manner.
This problem is solved by the invention in that between the drive housing and the adjacent pumping chamber an intermediate plate is provided, through which the shafts pass, which contain a discharge line brought out laterally, and which is removable from the wall of the drive housing. In this system, additional means for separating the drive chamber from the adjacent pumping chamber can be provided between the shafts and the intermediate plate according to the invention. It is preferable for the shafts to be equipped in this area with bushings, preferably piston-ring bushings. Another important advantage has to do with the use of the pump according to the invention with toxic media. Due to the intermediate plate the contaminated part of the pump is clearly definable and separable from a noncontaminated area.
Pumps of the kind according to the invention, preferably with vertically disposed shafts, are usually built up sectionally. Assembly begins with the drive housing, the gears, shafts and drive bearings. This work calls for great care and therefore it is tedious. Then the components and rotors forming the pumping chambers are placed over the shafts successively and then only have to be tightened. Through the use of the intermediate plate according to the invention the assurance is provided that the complicated assembly part of the pump, namely the drive housing, is not part of the contaminated area. The contaminated area is limited to the parts that are easy to remove and install. After the removal of the contaminated parts the parts subject to wear (bearings, shaft sealing ring) are easy to reach. The drive housing, as the component difficult to assemble, is protected both against contaminants and against wear. Overall, a greater ease and simplicity of service procedures are achieved by the invention.
Additional advantages and details of the invention are to be explained with the aid of embodiments represented in FIGS. 1 and 2.